Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/27070
Deprecate "chat commands" in favor of "slash commands"
We looked for things like:
- `slash commmand`
- `slash_command`
- `slash-command`
- `SlashCommand`
FFaker can generate data that randomly break our test suite. This
simplifies our factories and use sequences which are more predictive.
Signed-off-by: Rémy Coutable <remy@rymai.me>